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IC 8841 



Bureau of Mines Information Circular/1981 







■ 
■ 




The Noise Exposure of Operators 

of Mobile Machines 

in U.S. Surface Coal Mines, 1979 



By J. H. Daniel, J. A. Burks, R. C. Bartholomae, 
R. Madden, and E. E. Ungar 



UNITED STATES DEPARTMENT OF THE INTERIOR 






. ! 



Information Circular 8841 



The Noise Exposure of Operators 

of Mobile Machines 

in U.S. Surface Coal Mines, 1979 



By J. H. Daniel, J. A. Burks, R. C. Bartholomae, 
R. Madden, and E. E. Ungar 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 










This publication has been cataloged as follows: 



The noise exposure of operators of mobile machines in U.S. sur- 
face coal mines, 1979. 

(Information circular - Bureau of Mines ; 8841) 

Includes bibliographical references. 

Supt. of Docs, no.: I 28.27:8841. 

1. Coal-mining machinery— Noise. 2. Noise— Physiological effect. 
3. Coal mines and mining— United States— Safety measures. I. Daniel, 
J. H. II. Series: United States. Bureau of Mines. Information cir- 
cular ; 8841. 



TN295.U4 [TN813] 622s [363.7'41] 80-607786 AACR1 



CONTENTS 



Page 



Abstract 1 

Introduction 1 

Machine census 1 

Machine noise and operator exposure 5 

Noise control 9 

Major sources and paths 9 

Noise reduction of dies el -powered equipment 10 

Results of retrofit noise control in bulldozers 10 

Conclusions 14 

Appendix A. — Calculation of average working noise level 15 

Appendix B. --Working noise level data base 16 

ILLUSTRATIONS 

1. Caterpillar D9G bulldozer with rollover protective structure 12 

2. Caterpillar D9G bulldozer with full operator cab 13 

B-l. Working noise level of dozers 16 

B-2. Working noise level of loaders 18 

B-3. Working noise level of motor graders 19 

B-4. Working noise level of haulers 20 

B-5. Working noise level of scrapers 21 

B-6. Working noise level of drills 22 

B-7. Working noise level of wheel dozers 23 

B-8. Working noise level of electric shovels and draglines 24 

TABLES 

1. Ranking of machine types on basis of numbers in use 2 

2. Major machine models in use in U. S. surface coal mines 3 

3. Percentages of machines with cabs 4 

4. Noise exposures of machine operators 6 

5. Projected number of machines and overexposed operators in 

U. S . surface coal mines 8 

6. Summary of noise control treatments installed on dozer equipped 

with ROPS only (high idle) 11 

7. Summary of noise control treatments installed on dozer with cab 

(high idle, doors closed) 13 

A-l. Permissible noise exposures 15 



THE NOISE EXPOSURE OF OPERATORS OF MOBILE MACHINES 
IN U.S. SURFACE COAL MINES, 1979 

by 

J. H. Daniel, ] J A. Burks, 2 R. C. Bartholomae, 3 R. Madden, 4 
and E. E. Ungar 5 



ABSTRACT 

This report, summarizing the results of two studies sponsored by the 
Bureau of Mines, presents information on the types of mobile machines used in 
surface coal mines in the United States, and the amount of noise to which 
miners are exposed. Data consist of a calculated value of the probability of 
noise overexposure caused by specific equipment. These data are extrapolated 
to estimate the number of overexposed operators. Bulldozers were identified 
as the major contributors to noise overexposure, and the report presents 
results of a Bureau-funded program on the feasibility of providing retrofit 
noise control on bulldozers. 

INTRODUCTION 

Many mobile machines used in U.S. surface coal mines produce noise levels 
higher than those permitted by the Federal Coal Mine Health and Safety Act of 
1969 (Public Law 91-173) and the Federal Mine Safety and Health Amendments Act 
of 1977 (Public Law 95-164). Recognizing this problem, the Bureau of Mines 
sponsored two projects between 1976 and 1979 to identify and control noise 
levels from these machines. The first project was a census of the types and 
number of mobile machines in surface coal mines. This project involved noise 
measurements of mobile machines and an estimate of the total overexposure. 
The second project was to retrofit noise control of two heavy track bulldozers. 

MACHINE CENSUS 

Results from a combination of questionnaires and extrapolations show 
there were approximately 38,500 mobile machines in use at U.S. surface coal 

1 Program manager, Branch of Health Research, Bureau of Mines, Washington, D.C. 
3 Technical project officer, Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
Supervisory electrical engineer, Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
4 Manager, Mechanical System Analysis, Bolt, Beranek and Newman, Inc. , 

Cambridge, Mass. 
5 Principal engineer, Bolt, Beranek and Newman, Inc. , Cambridge, Mass. 



mines in 1977. Extrapolations were required because, although a questionnaire 
was mailed to every mine address on the Mine Safety and Health Administration 
(MSHA) and Bureau of Mines lists, not all mines responded. Two methods of 
extrapolation were used independently; one was based on production, and the 
other on survey response rate. Both yielded comparable results. 6 

Table 1, which lists the machines in order of the number in use, shows 
that two types dominate. Heavy track dozers (>150 hp) are the most numerous, 
accounting for more than 27 percent of all machines, and they are followed by 
heavy wheel front-end loaders, which account for more than 16 percent. 
Together, these two types account for about 43 percent of all machines used 
in surface coal mines. All types of dozers combined form nearly 30 percent 
of the total population, and all types of loaders form nearly 20 percent, 
together accounting for nearly one-half of all machines used in surface coal 
mines. 

TABLE 1. - Ranking of machine types on basis of numbers in use 



Rank 


Percent 


Cumulative 
percent 


Machine 




1 


27.3 


27.3 


Dozer, track, heavy. 




2 


16.4 


43.7 


Loader, wheel, heavy. 




3 


14.6 


58.3 


Hauler. 




4 


7.6 


65.9 


Truck, highway. 




5 


7.5 


73.4 


Shovels and draglines, internal 
power. 


combustion 


6 


4 


77.4 


Scraper, tandem. 




7 


3.8 


81.2 


Motor grader'. 




8 


3.4 


84.6 


Drill, blasthole, without cab. 




9 


3.3 


87.9 


Drill, blasthole, with cab. 




10 


3 


90.9 


Scraper. 




11 


2.5 


93.4 


Loader, wheel, light. 




12 


1.7 


95.1 


Dozer, track, light. 




13 


1.3 


96.4 


Shovels and draglines, electric, 


<30 cu yd. 


14 


1.0 


97.4 


Shovels and draglines, electric, 


>30 cu yd. 


15 


.8 


98.2 


Auger, coal, high-wall. 




16 


.8 


99 


Loader, track. 




17 


.5 


99.5 


Dozer, wheel. 




18 


.3 


99.8 


Drill, coring, truck -mounted. 





NOTE. --Heavy = 150 hp or more; light = less than 150 hp. 



'Ungar, E. E. 



A Census of Mobile Machines Used in U.S. Surface Coal Mines, 



BuMines Open File Report 78-077, 1977, 174 pp. (Contract J0166057) ; avail- 
able for consultation at the Bureau of Mines libraries in Denver, Colo. , 
Twin Cities, Minn., Bruceton and Pittsburgh, Pa., and Spokane, Wash.: at 
the Department of Energy facilities in Carbondale, 111. , and Morgantown, 
W. Va. ; and the National Library of Natural Resources, U.S. Department of 
the Interior, Washington, D.C.; and from the National Technical Information 
Service, Springfield, Va. , PB 284 112/AS. 



Table 2 lists the predominant manufacturers of each major machine category, the pre- 
dominant models in use, and the percentage of these models in each category. For example 
the table shows that Caterpillar dominates the dozer category: Caterpillar manufactures 
71 percent of all dozers used in surface coal mines, 47 percent of which are Caterpillar 
model D9. Caterpillar also manufactures 46 percent of all front-end loaders used in sur- 
face coal mines, 18 percent of which are Caterpillar model 988. 

TABLE 2. - Major machine models in use in U.S. surface coal mines 

(see text footnote 6) 









Percent 








Percent 








of 








of 


Machine 


Manufacturer 


Model 


machine 
type 

popula- 
tion 


Machine 


Manufacturer 


Model 


machine 
type 

popula- 
tion 


Dozers. . . 


Caterpillar 


D9 


47 


Highway 


Ford 


F100 


4 






D8 


17 


trucks. 




F600 


4 






All 


71 






All 


28 




International. . . . 


TD25 


11 




Mack 


600 


4 






All 


12 






685 


3 




Allis-Chalmers. . . 


All 


7 




General Motors. . . 


All 
All 


18 

12 


Loaders. . 


Caterpillar 


988 


18 




Chevrolet 


All 


11 






992 


10 




International. . . . 


All 


10 




Hough 


All 
All 


46 
13 




White 


All 


8 










Michigan 


All 


13 


Scrapers. 


Caterpillar 


637 


18 




International. . . . 


All 


6 






631 
657 


12 
7 


Haulers . . 


Euclid 


All 
773 


32 
10 




Terex 


All 
T524 


55 




Caterpillar 


16 






All 


18 






All 


25 




International. . . . 


All 
All 


12 
10 




Euclid 


All 


5 












All 


8 


Blasthole 


Gardner-Denver. . . 


RDC16 


10 




Dart 


All 


5 


drills. 


Bucyrus-Erie 


All 
50R 


15 
5 


Shovels. . 


Bucyrus-Erie 


All 


26 






All 


14 




Marion 


All 


19 




Chicago Pneumatic 


650 


9 




Lorain 


All 
800 
All 


11 
4 
9 




Robbins 


All 
All 
All 


13 






13 




Ingers oil-Rand. . . 


11 




Lima 


All 
3500 


8 

4 


Graders. . 




12 








28 






All 


8 






16 

14 


22 
16 


Draglines 




4600 


13 






All 


72 






4500 
All 


8 
25 




Gal ion 


All 


12 












88B 

All 


9 
25 












Lima 


2400 
All 


13 
18 


















Marion 


All 


12 














All 


9 











NOTE. 



-All refers to all of the manufacturer's models in use. 



An obvious first step in reducing noise exposure is the use of operator 
cabs. Table 3 gives the percentages of machines that have cabs, the size of 
the mine in which the machine is operated, and whether the cab has any form of 
noise control (acoustical) treatment. As the table shows, 70 percent of all 
machines have cabs, nearly one-half of these machines with cabs have some kind 
of acoustical treatment, and there are more cabs in large mines than in small 
mines. In addition, there are more acoustically treated cabs on newer machines 
than on older equipment; acoustically treated cabs came into significant use 
between 1969 and 1972. 

TABLE 3. - Percentages of machines with cabs 



Machine 



Percent with cab 
of any kind 



Large 
mines 



Small 
mines 



All 
mines 



Percent with 
acoustical cab 



Large 
mines 



Small 
mines 



All 
mines 



Dozer, track, heavy 

Loader, wheel, heavy 

Hauler 

Truck, highway r . 

Shovels and draglines, internal com- 
bustion power 

Scraper, tandem 

Motor grader 

Drill, blasthole 

Scraper 

Loader, wheel , light 

Shovels and draglines, electric, 
<30 cu yd 

Shovels and draglines, electric, 
>30 cu yd 

Dozer, track, light 

Auger, coal, high -wall 

Loader, track 

Dozer, wheel 

Drill, coring, truck-mounted 

Total 



58 
67 
25 
97 

85 
62 
60 
50 
53 
61 

91 

89 
63 
18 
65 
83 
46 



57 
70 
86 
92 

83 
52 
64 
50 
27 
56 

80 

60 
45 
18 
41 
50 
50 



57 
62 
93 
96 

78 
60 

61 
50 
47 
59 

89 

86 
57 
18 
50 
81 
47 



35 

44 

57 

5 

33 
30 
32 
22 
24 
41 

59 

62 
36 

3 
27 
56 





29 

44 
34 
10 

19 

15 

30 

18 

8 

26 

25 

30 
29 
2 
15 
50 
17 



32 

44 

53 

7 

26 
26 
32 
22 
21 
35 

54 

58 
28 

2 
20 
55 

3 



72 



60 



70 



37 



30 



34 



NOTE. --Large = production 100,000 tons per year or more; small = production 
less than 100,000 tons per year; heavy = 150 hp or more; light = less 
than 150 hp. 



MACHINE NOISE AND OPERATOR EXPOSURE 

A major objective of the research was the calculation of the noise expo- 
sure of operators of various machines. 7 For this calculation, independent 
estimates were made of the average working noise level and the time of opera- 
tion. The average working noise level was defined as that constant noise 
level that, if present during the entire work cycle, would result in the same 
noise exposure, or dose, resulting from fluctuating noise levels that actually 
occur. Computation of the average working noise level requires the typical 
work cycle to be divided into a number of events, each of which can be defined 
in terms of a typical noise level and percentage of the work cycle; for exam- 
ple, for a dozer, the typical work cycle consists of dozing, transporting, and 
backing. It is, in fact, equivalent to the level read from a noise dosimeter 
measuring noise over one work cycle. An example of the calculation is pre- 
sented in appendix A, and details of the procedure are given in footnotes 6 
and 7. 

Data on machinery noise, work cycles, machine usage durations, and shift 
lengths were collected during visits to nine mines that included both large 
and small operations, located in the Appalachian, Midwestern, and Western 
regions. Data on the noise and work cycles of over 80 individual machines 
were obtained by direct measurement, and these data were supplemented by infor- 
mation extracted from interviews with mine personnel. Additional data were 
gathered from study reports made available by some mines, from the literature, 
and from a sample of records submitted by mine operators to one of the MSHA 
district offices. 

Operator exposures were evaluated on the basis of the most reliable data 
available. Where possible, noise data measured in this program were used. 
For machine types for which information was inadequate, estimates were based 
on data in the literature of the MSHA records. Daily exposure durations were 
taken directly from the MSHA data. 

Table 4 shows the mean values and standard deviations of the average work- 
ing noise levels of the operators of various machines, daily operator exposure 
durations, and the probabilities of operator overexposure. The data base from 
which these values are taken is presented in appendix B. A distinction is 
made to the extent allowed by available data between machines with no cabs, 
conventional cabs, and acoustical cabs. 



7 Ungar, E. E. , D. W. Andersen, and M. N. Rubin. The Noise of Mobile Machines 
Used in Surface Coal Mines: Operator Exposure, Source Diagnosis, Potential 
Noise Control Treatments. BuMines Open File Report 79-098, August 1978, 
114 pp. (contract J0166057) ; available for consultation at the Bureau of 
Mines libraries in Denver, Colo., Twin Cities, Minn., Pittsburgh, Pa., and 
Spokane, Wash.; at the U.S. Department of Energy facilities in Carbondale, 
111., and Morgan town, W. Va. ; at the National Mine Health and Safety 
Academy, Beckley, W. Va. ; at the National Library of Natural Resources, 
U.S. Department of the Interior, Washington, D.C.; and from the National 
Technical Information Service, Springfield, Va. , PB 299 538/AS. 



TABLE 4. - Noise 


exposures of machine operators 


(see text j 


cootnote 7) 






















Cab 1 


Average working 
noise level, dBA 3 


Daily exposure 
duration, hours 4 


Overexposure 
probability, percent 


Machine 


Mean 


Standard 
deviation 


Mean 


Standard 
deviation 3 


Present 
criterion 5 


5 -dBA -More 

stringent 

criterion 


Dozers, track, ^150 hp. . . . 


N 
C 
A 


103 
98.5 
92.6 


1.5 
3.0 
4.5 


6.0 
6.0 
6.0 


2.8 
2.8 
2.8 


96 
88 

49 


99 
96 
80 


Dozers, track, <150 hp. . . . 


T 


94(L) 


3.5(L) 


5.7 


3.5 


57 


83 


Dozers , wheel 


N 
C 
A 


96(E) 

96.5 

92 


5.0(E) 

2.0 

6.0 


4.2 
4.2 
4.2 


2.0 
2.0 
2.0 


55 
65 
32 


81 
90 
60 


Loader, wheel, >150 hp. . . . 


N 
C 
A 


94.5 
93.5 
84.6 


1.5 
5.0 

4.5 


6.3 
6.3 
6.3 


3.0 
3.0 
3.0 


74 
56 
5.9 


93 
82 
29 


Loader, wheel, <150 hp. . . . 


T 


97(1) 


3.0(I,E) 


5.9 


3.2 


79 


93 


Loader, track 


T 


91.5(L) 


4.0(L,E) 


5.5 


3.8 


37 


69 


Hauler 1 . . . 


T 

T 


88.5 
85(E) 


4.5 
5.0(E) 


6.1 
3.6 


2.5 
2.0 


23 
2.6 


57 




14 


Scraper, tandem 


N 
C 
A 


92(E) 
91.5 

85 


7.0(E) 
7.0 
.5 


5.6 
5.6 
5.6 


2.3 
2.3 
2.3 


44 

41 




69 




67 

14 




N 
C 
A 


96(E) 

95.5 

91 


5.0(E) 

3.5 

5.0(E) 


5.8 
5.8 
5.8 


2.6 
2.6 
2.6 


69 
71 
37 


89 
92 
69 


Motor grader 


N 
C 
A 


96(E) 

95.8(1) 

86.5 


5.0(E) 
4.0(1) 
5.0 


5.1 
5.1 
5.1 


3.1 
3.1 
3.1 


62 
64 
11 


84 




86 
35 


Shovels and draglines, 


T 


77.5 


6.5 


5.3 


1.5 


1.2 


6.2 


Shovels and draglines, 


T 


86 


4.0 


5.8 


2.3 


6.7 


35 


Shovels and draglines, 
internal combustion power 


T 


91 


6.5 


5.9 


3.7 


38 


64 


Drill, blasthole 


N 
C 
A 


90 
85 
83 


2.0 
5.0 
3.0 


5.6 
5.1 
5.1 


2.5 
2.7 
2.7 


20 
7.2 
.2 


70 
27 
7.8 


Drill , coring 


T 


87(E) 
95(E,M) 


5.0(E) 
5.0(E) 


5.4 


2. 8 


14 


40 


Auger 


T 


4.1 


2.0 


48 


76 







1 A Acoustical cab, C Nonacoustical cab, N No cab, T All conditions. 

3 Based on Bolt, Beranek and Newman and verified mines data, except as otherwise specified: 

E Estimated, I Includes literature data, L From literature, M Includes MSHA data. 

Values are rounded off to nearest 0.5 dBA. 
3 About 70 percent of all values may be expected to fall within 1 standard deviation below 

and above the mean. 
4 Values are rounded off to nearest 0.1 hour. 
5 90 dBA permissible for 8 hours daily; a reduction factor of 

sure duration for each 5-dBA increase above 90 dBA. 
"85 dBA permissible for 8 hours daily; a reduction factor of 

sure for each 5-dBA increase above 85 dBA. 



in permissible daily expo- 
in permissible daily expo- 



The overexposure probabilities indicate the fractions of the total opera- 
tor population that suffer overexposure according to the given criteria. 
These probabilities provide no information about how often (what fraction of 
the time) the exposure of the operator of a given machine exceeds the permis- 
sible limit. These overexposure probabilities are given for two criteria. 
The first criterion is a regulation specified in the Coal Mine Health and 
Safety Act of 1969, which permits exposure to 90 dBA for 8 hours per day and 
prescribes a reduction by a factor of 2 in the permissible daily exposure dur- 
ation for each 5-dBA noise level increment above 90 dBA. The second, more 
stringent, criterion permits exposure to 85 dBA for only 8 hours per day and 
again prescribes an exposure duration reduction for a factor of 2 for each 
5-dBA increment. 

As shown in table 4, operators of heavy track dozers without cabs are 
exposed to mean working noise levels of 103 dBA for a mean of 6 hours per day. 
The last two columns of the table show that 96 percent of the operators of 
dozers without cabs in surface coal mines are overexposed to noise, according 
to the current Federal regulations. If the 5-dBA -more stringent criterion is 
adopted, 99 percent of the operators are overexposed. The procedure for cal- 
culating the overexposure probability is given in footnote 7. 

Table 4 also shows that when cabs — particularly cabs with noise control 
treatments — are used on any type of machine, they decrease both working noise 
levels and the probability of overexposure. 

For each of the various types of machines used in U.S. surface coal mines, 
table 5 shows the total number of machines in use (based on projections devel- 
oped from the census data) , the average number of people operating each machine 
per day (based on the average number of daily shifts the machines are in use, 
according to the machine census) , and the number of operators in all U.S. sur- 
face coal mines who may be expected to be overexposed (according to both the 
current criterion and the more stringent criterion). The last two columns 
also show the percentages (in parentheses) of the total number of operators, 
approximately 56,200, who suffer overexposure. 

This table gives two important statistics. According to the present cri- 
terion, over 25,000 operators, or nearly 45 percent of all mobile machine oper- 
ators in U.S. surface coal mines, are overexposed to noise. With the more 
stringent criterion, the number of operators overexposed to noise increases 
to over 37,000, or more than 66 percent of the entire operator population. 

Table 5 also shows that all types of dozers together are responsible for 
overexposure of over 13,500, or nearly 24 percent of all surface mine opera- 
tors; that is, dozers contribute more than 50 percent of all noise overexpo- 
sures. Loaders, in turn, overexpose more than 4,700 operators, or 8.6 percent 
of all surface mine operators, and they account for slightly less than 19 per- 
cent of all noise overexposures. 



TABLE 5. - Projected number of machines and overexposed operators 
in U.S. surface coal mines (see text footnote 7) 









Average number 


Number of overexposed 




Cab 1 


Number of 
machines 3 


of operators 
per day per 


operators 3 


Machine 


Present 


5-dBA-More 








machine 2 


criterion 4 


stringent 
criterion 5 




N 


4,551 


1.56 


6,816 (12.1) 


7,028 (12.6) 




C 


2,648 


1.56 


3,635 (6.5) 


3,966 (7.1) 




A 


3,447 


1.56 


2,635 (4.7) 


4,302 (7.7) 


Dozer, track, <150 hp 


T 


584 


1.34 


446 (.8) 


649 (1.2) 




N 


24 


1.92 


25 (-) 


37 (.1) 




C 


32 


1.92 


40 (.1) 


55 (.1) 




A 


71 


1.92 


44 (.1) 


82 (.1) 


Loader, wheel, >150 hp 


N 


2,149 


1.36 


2,163 (3.8) 


2,718 (4.8) 




C 


1,661 


1.36 


1,265 (2.2) 


1,852 (3.3) 




A 


2,991 


1.36 


240 (.4) 


1,179 (2.1) 


Loader, wheel, <150 hp 


T 


1,033 


1.30 


1,061 (1.9) 


1,249 (2.2) 




T 


411 


1.13 


172 (.3) 


320 (.6) 


Hauler 


T 
T 


5,620 
2,939 


1.52 
1.25 


1,965 (3.5) 
95 (.2) 


4,869 (8.7) 




514 (.9) 


Scraper tandem 


N 


462 


1.47 


299 (.5) 


469 (.8) 




C 


393 


1.47 


237 (.4) 


387 (.7) 




A 


310 


1.47 


(-) 


64 (.1) 




N 


486 


1.33 


'446 ( . 8) 


575 (1.0) 




C 


252 


1.33 


238 (.4) 


308 (.5) 




A 


197 


1.33 


97 (.2) 


181 (.3) 


Motor grader 


N 
C 


549 

411 


1.19 

1.19 


405 (.7) 
313 (.6) 


549 (1.0) 




421 (.7) 




A 


450 


1.19 


59 (.1) 


187 (.3) 


Shovels and draglines, 












electric, £30 cu yd 


T 


234 


3.14 


9 (-) 


46 (.1) 


Shovels and draglines, 














T 


334 


2.20 


49 (.1) 


257 (.5) 


Shovels and draglines, 












internal combustion power. 


T 


3,273 


1.45 


1,803 (3.2) 


3,037 (5.4) 


Drill, blasthole 


N 


1,316 


1.20 


316 (.6) 


1,105 (2.0) 




C 


721 


1.75 


91 (.2) 


341 (.6) 




A 


558 


1.75 


2 (-) 


76 (.1) 


Drill , coring 


T 
T 


109 
323 


1.47 
1.53 


22 (-) 
237 (.4) 


64 (.1) 




376 (.7) 


Total 


NAp 


38,539 


NAp 


25,225 (44.9) 


37,263 (66.3) 




NAp 


NAp 


1.46 


NAp 


NAp 



NAp Not applicable 

X A Acoustical cab, C Nonacoustical , N No cab, T Total, al 

8 Based on text footnote 6. 

3 Figures in parentheses indicate percentage. Projected total 

(-) = less than 0.1 percent. 
4 90 dBA permissible for 8 hours daily; a reduction factor of 

sure duration for each 5-dBA increase above 90 dBA. 
5 85 dBA permissible for 8 hours daily; a reduction factor of 

sure duration for each 5-dBA increase above 85 dBA. 



1 conditions. 

number of operators = 56,226; 

2 in permissible daily expo- 
2 in permissible daily expo- 



The next most significant categories lag far behind dozers and loaders. 
They are haulers, which overexpose nearly 2,000 operators (3.5 percent of all 
operators, 8 percent of all overexposed operators) and diesel-powered shovels 
and draglines, which overexpose about 1,800 operators (3.2 percent of all 
operators, 6 percent of all overexposed operators). 

Two facts should be noted, because they have a bearing on the overexpo- 
sures shown in table 5. Most of the overexposure associated with haulers 
results from haulers being operated with open windows; haulers whose noise is 
measured with their windows closed rarely present a noise overexposure problem. 
Similarly, the data base for shovels and draglines powered by internal combus- 
tion engines is biased toward older models because newer models tend to be 
much quieter. As a result, the overexposures indicated for haulers and for 
shovels and draglines may be overestimated. 

NOISE CONTROL 

The extent of operator overexposure and the types of mobile machines 
responsible for that overexposure, the results of the first study, were pub- 
lished in a Bureau of Mines report in 1978 (see footnote 7). Following this 
study, the Bureau sponsored additional research to retrofit noise control on 
two representative machines from the category that had been identified as the 
most numerous and the most noisy--heavy track bulldozers. Descriptions of 
this project are prefaced by a general discussion of noise control techniques-- 
the "tools" of noise control. 

Major Sources and Paths 

In general, the noise from any one source reaches the ear via several 
paths, both directly, by airborne paths, and indirectly, by reflections from 
various surfaces. In addition, sound in the form of vibrations may travel 
along or through structures. 

In diesel-powered mining equipment, the engine is generally a major 
source of noise. Engine noise may come from the exhaust, the intake, and the 
casing (that is, the block and accessories attached to it) --as well as the 
cooling fan--often a significant noise source. The transmission, drive train, 
and hydraulic system also tend to be significant noise sources. 

Noise radiated from the various sources may reach the operator by propa- 
gating through the air, directly or by reflections. In addition, vibrations 
produced by the engine and other mechanical components, as well as structural 
vibrations caused by sounds, tend to propagate along machine structures, thus 
causing these structures to radiate sound, somewhat like a loudspeaker. 

The relative importance of the various noise sources and paths differs 
for different machine types and models. One fact is basic for all machines, 
however: Just as repair of small holes in a leaking roof is useless if large 
holes are left open, reducing the noise of lesser sources and paths has prac- 
tically no effect on a worker's exposure unless the contributions from the 
major sources and paths are reduced. In addition, it does not usually make 



10 



sense to spend that money to quiet dominant sources and paths to the point 
where their contributions are far below those of the lesser sources and paths. 
Overquieting is both impractical and costly. 

Noise Reduction of Diesel-Powered Equipment 

In general, the noise exposure of an operator of a given machine may be 
reduced by blocking the paths of sound between the important noise sources and 
the miner. Usually, for both practical and economical reasons, the primary 
noise sources cannot be modified or replaced with quieter ones (except rela- 
tively early in the development of new machines). Generally, then, the first 
solution to a problem of mine machine noise is blocking the noise paths, both 
airborne and structureborne. 

Cabs generally are the most efficient way to obstruct the radiation of 
sound from such sources as engines or transmissions. The effectiveness of 
such an enclosure increases with the mass of its walls, and effectiveness is 
greater if the cab is lined with some kind of acoustically absorptive material. 
If a full cab would .present problems of cooling or access, partial cabs or 
barriers may be used. They tend to be considerably less effective in noise 
reduction than full cabs because they do not provide the operator with noise 
attenuation from all directions which increases the operator exposure to both 
direct and reflected noise. In a partial cab, the noise the operator hears 
is not passing through it, but traveling around it. As a result, increasing 
the mass of the barrier (an effective way to reduce noise heard in full cabs) , 
usually results in little noise reduction in partial cabs. 

Mufflers obstruct the propagation of sound out of pipes or ducts, primar- 
ily by reflecting some of the sound back toward the source so that the 
reflected pressure waves almost cancel out the outgoing waves. It is impor- 
tant to match engine exhaust mufflers to the engine, so that they will be 
effective acoustically, yet not produce excessive backpressure. Mufflers are 
commercially available for almost all pieces of equipment used in U.S. surface 
mines. 

One of the most overlooked ways to reduce noise levels is machine mainte- 
nance. Table 4 shows a number of machine categories, such as highway trucks, 
with standard deviations of 4 dBA or more. This is a significantly large var- 
iation between the noise of one machine and another in the same category. 
There could be several reasons, of course, but experience has shown that a 
major contribution is the state of repair of the individual machine. Are the 
seals tight? Are all windows in place? Is the air conditioner working so the 
operator will not need to open the windows (letting in air and also noise)? 
Are the floormats in place? Proper maintenance of the machine is a must for 
successful noise control. 

RESULTS OF RETROFIT NOISE CONTROL IN BULLDOZERS 

In 1978, the basic principles of noise control described previously were 
used to quiet two heavy track Caterpillar D9G bulldozers. One had a rollover 
protective structure (ROPS) only and no operator cab, and the other was 



11 



equipped with a standard cab. Before the program, the high-idle sound level 
at the operator position for the dozer with ROPS only was 105.5 dBA. The 
noise of the dozer with the cab, under similar high-idle conditions with the 
doors closed, was measured at 100 dBA. Once the noise control treatments were 
installed, noise levels at high idle were reduced 11.5 and 12 dBA, correspond- 
ing to sound levels of 94 and 88 dBA, respectively, for the two dozers. 

Figure 1 shows the dozer that was equipped with ROPS only, with all noise 
control treatments installed. Visible in the photograph are the muffler and 
the Lexan 8 windshield, which were installed to block airborne noise from the 
engine and the fan. The treatments are itemized in table 6, together with the 
noise reduction the treatment provides at high idle. About 6 dBA of reduction 
was obtained by applying three major treatments, windshield, muffler, and 
sound absorption under the ROPS canopy. The remaining 5.5 dBA of reduction 
was obtained by carefully sealing openings and by isolating the dash from 
engine vibrations. Materials for the entire treatment package cost less than 
$1,000 in 1978. 

TABLE 6. - Summary of noise control treatments installed on dozer 

equipped with ROPS only (high idle) 







Sound level, 


Noise reduction 




Treatment 


dBA 


from 


baseline, 
dBA 


1. 




105.5 







2. 




101.5 




4 


3. 




102.5 




3 


4, 


Exhaust muffler 


104 
100 
99.5 




1.5 


5 


Windshield and absorption 


5.5 


6. 


Windshield, absorption, and muffler 


6 


7. 


Windshield, absorption, muffler, and dash 










seals and isolation 


96.5 




9 


8. 


Windshield, absorption, muffler, dash seals 








95.5 




10 


9. 


Windshield, absorption, muffler, dash seals 










and isolation, floor seals and seat seals. 


95 




10.5 


10. 


Windshield, absorption, muffler, dash seals 
and isolation, floor seals, seat seals, 










tank seal, and hydraulic valve cover 


94 




11.5 



s Reference to specific trade names or equipment does not imply endorsement by 
the Bureau of Mines. 



12 




FIGURE 1. - Caterpillar D9G bulldozer with rollover protective structure. 

The dozer with the cab is shown in figure 2; all noise control treatments 
are installed inside the cab. Table 7 lists the treatments, most of which are 
the same as those previously discussed. Exceptions are seals between the cab 
walls and the floorboards and the inclusion of additional absorptive material 
on the fuel tank, on the hydraulic tank cover, and under the dash. The total 
cost of materials for this package was also less than $1,000 in 1978. 



When the noise control treatments were completed, the dozers were placed 
in service during March and April 1978. Both are currently (1980) operating 
at surface coal mines in the Eastern United States. 



13 



TABLE 7. - Summary of noise control treatments installed on dozer 

with cab (high idle, doors closed) 



Treatment 




Noise reduction 
from baseline, 
dBA 



1 . None (baseline) 

2. Absorption under ROPS 

3. Cab wall seals and absorption 

4. Absorption, cab wall seals, floormats, and 

pedal seals 

5. Absorption, cab wall seals, floormats, pedal 

seals, seat seals, hydraulic tank cover 
seals, and blade control seal 

6. Absorption, cab wall seals, floormats and 

pedal seals, seat seals, hydraulic tank 
seal, blade control seal, and dashboard 
isolation 




2 
2.5 

4.5 



6.5 



12 



Noise dosimeter readings taken at the operator position on the dozer with 
ROPS only indicate that the time-weighted average noise is 93.5 dBA, with a 
standard deviation of 4 dBA during normal operation. This noise level indi- 
cates that the dozer will be in compliance with the Federal regulations, with- 
out requiring hearing protection for the operator, for operation of 4-1/2 to 
5-1/4 hours per day. Dosimeter readings taken on the dozer with cab give the 




FIGURE 2. - Caterpillar D9G bulldozer with full operator cab. 



14 



time -weigh ted average as approximately 90 dBA. This dozer can, therefore, be 
in compliance for full-shift operation. 

Subsequent inspection visits indicated that these reduced noise levels 
can be maintained through relatively minor maintenance, primarily of the 
elastomeric seals. 

CONCLUSIONS 

The noise exposure of U.S. surface coal miners was evaluated in this 
Bureau report. A 1977 study indicated that over 25,000 mobile machine opera- 
tors (nearly 45 percent of the approximately 56,200 operators) were over- 
exposed to noise according to the criterion specified in the Federal Coal 
Mine Health and Safety Act of 1969 and the subsequent Amendments of 1977. 
Heavy track dozers were the largest contributors, responsible for 54 percent 
of the overexposure, and rubber- tired front-end loaders were second in impor- 
tance, contributing 19 percent of the overexposure. On the basis of these 
results, the Bureau selected bulldozers for a demonstration of the feasibility 
of retrofit noise control. The two dozers that were chosen were a Cater- 
pillar D9G with ROPS only and a D9G with a cab. The noise from the dozer 
equipped with ROPS only was reduced by 11.5 dBA, and the noise from the dozer 
with the cab was reduced by 12 dBA. 



15 



APPENDIX A.— CALCULATION OF AVERAGE WORKING NOISE LEVEL 

The average working noise level is a useful concept for characterizing 
the noise exposure contribution of a given machine that produces nonconstant 
noise levels. The average working noise level is defined as the constant 
noise level that results in the same noise dose as the actual nonconstant 
noise levels, for the period the machine is operating. 

For example, consider a machine that subjects its operator to 90 dBA 
while it idles and to 95 dBA while it is used at full power; assume also that 
the machine operates at idle for 30 percent of the time it is in use and at 
full power 70 percent of the time. Note from table A-l that the permissible 
exposure duration for 90 dBA is 8 hours and for 95 dBA, 4 hours. Assuming a 
total of 7 hours of use per day (7 X 0.30 = 2.10 hours at 90 dBA and 7 X 0.70 
= 4.90 hours at 95 dBA), a total noise dose of 2.10/8 + 4.90/4 = 1.487 is 
obtained. The average working noise level in this case is that noise level 
producing a noise dose of 1.487, if it is continuous for 7 hours. 

The permitted exposure duration T in hours is related to the noise dose D 
and actual exposure duration C in hours as 

T = C/D. (A-l) 

Thus, there the permitted duration T is 7/1.487 = 4.71 hours. From the values 
indicated in table A-l, one may observe that the average working noise level 
is between 92 and 95 dBA. The exact value of 93.8 dBA can be calculated from 
equation A-2 in table A-l. 

The assumed value of the daily use time (taken above as 7 hours) does not 
affect the value of the average working noise level. The effects of the 
assumed values of the daily use time cancel, because the same number is used 
in the dose evaluation calculation and in the determination of the correspond- 
ing permitted duration. 

TABLE A-l. - Permissible noise exposures 



Duration of exposure 


Noise level, 


Duration of exposure 


Noise level, 


per day, hours 


dBA 


per day, hours 


dBA 


8 


90 


1.5 


102 


6 


92 


1 


105 


4 


95 


0.5 


110 


3 


97 


0.25 


115 


2 


100 







NOTE. — Noise levels are measured with a sound level meter set to slow 
response. Exposure to continuous levels above 115 dBA is not 
permitted by law. Values between those tabulated may be 
obtained from 



T = 



8 



2 (L-90)/ 5 



(A-2) 



where T denotes the daily exposure duration in hours, and L is 
the noise level in dBA. 



16 



APPENDIX B.— WORKING NOISE LEVEL DATA BASE 



MAKER MODEL CAB 



85 



AVERAGE WORKING NOISE LEVEL. dBA 
90 95 100 105 



110 



CAT 


D8 


N 
C 
A 
U 


1E bl 






1^)1 




3| 








r 


CAT 


D8H 


N 
C 
A 
U 








I 


12 


:uws;/////;/;//a 




I 


i 


v///////Ay///////A\ 


I 




i 










CAT 


D9 


N 
C 
A 
U 






£% 


□ 3 




VV/////W/AWA 




*1>/AW///A 


\- 






I I 






I I 


|)11 



Notes. 



Average minus Average plus 

standard deviation standard deviation 
Average 

t 



Doors and/or windows 



M 



Closed 

Open, absent, 
or status unknown 



Numbers next to bars indicate samples in data base. (When data for only one sample are available, 
no standard deviation can be calculated; bar is arbitrarily shown 1 dB long, centered on average value. 

Manufacturers' abbreviations 



ALC 


Allis-Chalmers 


GTS 


Gates 


BAT 


Bates 


GMC 


General Motors 


BUC 


Bucyrus-Erie 


HGH 


Hough 


CAT 


Caterpillar 


IHC 


International 


CHP 


Champion 


JOY 


Joy 


CGP 


Chicago Pneumatic 


KOM 


Komatsu 


CLK 


Clark 


KRS 


Kress 


DRT 


Dart 


LMA 


Lima 


DVY 


Davey 


LOR 


Lorain 


DLT 


Drill tech 


LTN 


LeTourneau 


EUC 


Euclid 


MCK 


Mack 


FIA 


Fiat-Allis 


MTC 


Manitowoc 


GRD 


Gardner-Denver 


MRN 


Marion 


KEY 






A = Acoustical cab 






C = Nonacoustical cab 






N = N 


)ne 






U = U 


nknown MSHA data sample 








FIGURE B-l. - Working noise leve 



MSF 


Massey-Ferguson 


MGN 


Michigan 


NWT 


Northwest 


PGE 


Page 


PRS 


Parsons 


ROB 


Robbins 


SLM 


Salem 


SRD 


Schroeder 


TRX 


Terex 


TJN 


Trojan 


UNT 


Unit Rig 


WAB 


Wabco 



17 



MAKER MODEL CAB 



85 



AVERAGE WORKING NOISE LEVEL, dBA 
90 95 100 105 



110 



CAT 


D9G 


N 
C 
A 
U 








I 
\ 






I 16 


31 


Y//////^///////A 


L 


iv;////#///////;//A 


\ 




i i 






1 1 






CAT 


D9H 


N 
C 
A 
U 


vmi jlj, 




□ 




i_T 












ALC 


HD-41 


N 
C 
A 
U 




6E 


T?fea2 


4 




1 1 1 




IHC 


TD-25C 


N 
C 
A 
U 






2CZD 






1 r 1 


KOM 
TRX 
TRX 


155-H 
82-40 
82-50 


U 
U 
U 




i 




12 


1 12 


i 




■ i 




| 1 \'J 








All 


N 
C 
A 
U 












4 


I I 11 
116 


14|^^^t%^Wj 


-y*immb 


Y////^//////////^///A |1d 






1 


i 1 i, :■ ;■ .. 








Total 












1 









FIGURE B-l. - Working noise level of dozers.— Continued 



18 



MAKER MODEL CAB AVERAGE WORKING NOISE LEVEL dBA 

85 90 95 100 105 110 


CAT 


966 


N 
C 
A 
U 




DD2 


» 






CAT 


988 


N 
C 
A 
U 


1 r^ 1 








ifcd ' 




1 . 1! .. _. «/ 








CAT 


992 


N 
C 
A 
U 


3E3 










*V//////////////s 


{ «r„Y« f «r„ n ( 


ni 1 




1 II 17 








IHC 


440 


N 
C 
A 
U 


□ 1 


n~i2 








LTN 


L700 


N 
C 
A 
U 












WJMMWsJ/A. 




l_ji 




MGN 
(CLK) 


475B 
A 


N 
C 

u 


ia 


e^i 

□ 1 








4| 


i i 


CLK 
CAT 
CAT 
HGH 


125B 

950^ 

980B 

560 


N 
C 
A 
U 


□ 1 




ni FT 






I I I: h 






All 




N 
C 












I I 


W/^////^ 7 


/ 


X Y////// 


w///< 


^//X^///////////////Z. 


\ 7 








u 


I l 


r5 




i. i 


_]16 






i 






Total 






' 1 ' ■ '" 



See figure B-1 for definitions of symbols 
-^ 130- hp machine, all others have over 150 hp 

FIGURE B-2. - Working noise level of loaders. 



19 



MAKER MODEL CAB 



80 



85 



AVERAGE WORKING NOISE LEVEL. dBA 
90 95 



See figure B-1 for definitions of symbols 

FIGURE B-3. - Working noise level of motor graders. 



100 



105 



CAT 
CAT 
CAT 
CAT 

CAT 


12F 
14E 
16G 
16G 

16 


A 
C 
C 
A 

U 


E 


3 


o 






i 


-.1 


1 








All (excluding U' data) 


3d 


1 










\z 






Total 






(Excluding 'U' data) 


(Including 


hi , » 




I 


1 'II' riatal 











20 



MAKER MODEL CAB 



80 



AVERAGE WORKING NOISE LEVEL, dBA 
85 90 95 



100 



105 



CAT 

CAT 
EUC 
UNT 

UNT 
WAB 


660 

773 
CH120 
BD180 

M100 
65 


C 

C 
C 
C 

C 
C 








V77Z\ 




| | 


DRT 
MCK 
UNT 
WAB 
WAB 
IHC 


DW20 
M25X 
M120 

32 

75 
PH-180 


C 
C 
C 
C 








12 


3 


I I 12 


1 I! 




2 

• 

^2 


r 








> www/w;;;;;///, 


C 
U 


T i i > 






All 










13 






iiuWWM 


//////////A>///////////A 




i r 




















i i 




I 26 


1 





See figure EH for definitions of symbols 

FIGURE B-4. - Working noise level of haulers. 



21 



TYPE MAKER MODEL CAB 



85 



90 



AVERAGE WORKING NOISE LEVEL, 
95 100 



dBA 



105 



110 



T 

T 
T 
T 
T 
T 
T 


CAT 

IHC 
TRX 


627 

637 
637 
657 

433 
TS14 


□ic E 

AOl 
C 
A C 

U 
U 


i 


2 


> 

GD2 




1 


E11 
31 

3 


1^ 


I l i: 


r~^ 


i 


Z33 












T 
T 
T 




All 
All 
All 
















r. &SS/AVSS/AWAVSSS^^^^ 




A J 

u 1 












r 


' r- 


-J , ' 


T 


Total 




i 


1 1 ' 


MR 












S 
S 

s 
s 


CAT 


631 
633 
633 
641 B 


u 
c 

A 
C 




□ i 
□i 










r~^ 


i / 


O 






s 
s 
s 




All 


C 
A 
U 




□ 1 
□ i 




m\ 






l=T= ^ 


r— «' 


s 


Total 








h ' 


_I10 





S = Single-engine scrapers 
T = Tandem scrapers 

See figure B-1 for definitions of symbols 

FIGURE B-5. - Working noise level of scrapers. 



22 



MAKER MODEL CAB 
75 



AVERAGE WORKING NOISE LEVEL. dBA 
80 85 90 95 



See figure B-1 for definitions of symbols 

FIGURE B-6. - Working noise level of drills. 



100 



BUC 

GTS 
PRS 
ROB 

SDR 


45R 

50R 
61R 

2HD 

RR10 
HORIZ 


C 
A 
U 
C 
U 

C 
C 
C 
A 
C 


?f#^^^^%!44^ 






^1 


^1 L 
CZJ1 


pn 


I I l 






i \y 




V////JXM 




2 


1 1 






I i \y 




All (with cabs) 


C 
A 
U 


V////////)/////^^^^^^ 








2 


1 -J 




yS>AMMW/MM//, :: 






I I 


Ih 


Total 






1 


1 


119 










CGP 
DVY 
JOY 


650 
35M 
225A 


N 
N 
N 






□ 1 
1CZD 


□ 1 




All (without cabs) 






I I 


la 









23 



MAKER MODEL CAB 



85 



90 



AVERAGE WORKING NOISE LEVEL, dBA 
95 100 



105 



See figure B-1 for definitions of symbols 

FIGURE B-7. - Working noise level of wheel dozers. 



110 



CAT 


824B 
834 


C 
A 

C 

A 

U 


E§3 

ES31 


1 

CD 




3 




1 \'A 




d 


1 










C 

A 
U 


ES3 


1 
□ 1 




3 




An 


f 


> 


1 I 'A 






B^K^a^^l ^ 








i 


1 






Total 












1 

1 


■- 


. 



24 

MAKER MODEL CAB 
85 



AVERAGE WORKING NOISE LEVEL, dBA 
90 95 100 105 



110 



I 
I 

30-ci 
BUC 
MRN 
MRN 
MRN 


1 
.ess than 

j-yd capa 
190B 
181 
183 
7400 


city 
C 
C 

c 
c 




CD 




T □ 

1 1 13 


All 












3t^#^^^W^I 




1 h 






Total 










l 


I I* 






i i 

30-cu-yd 
or greater capacity 












BUC 
BUC 
MRN 
MRN 
MRN 
PAH 
PGE 


1250 
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FIGURE B-8. - Working noise level of electric shovels and draglines. 






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